The invention relates generally to fluid flow control devices having a membrane valve and more particularly to an improved structure for restricting flow of the resilient membrane material under compression.
The invention is adapted for use in fluid control devices of the type herein described or as disclosed in U.S. Pat. Nos. 4,450,375 and 4,629,926.
These fluid flow devices include at least one cantilever mounted piezoelectrically operated actuator or bender which cooperates with an associated impacting member to cover and/or uncover a valve seat by deforming a resilient membrane. The valve seat is centered in a chamber and the impacting member and its associated bender is isolated from the fluid flow by the resilient membrane. The membrane is formed conventionally of a rubber or rubber-like material. The valve cover and valve housing are fastened together with the membrane under compression and the fluids dispensed are under pressure. Under these conditions, the membrane material tends to flow laterally between the assembled components. This leads to a thinning of the membrane and a flowing thereof over the valve seat area. The resulting thickening or bulging of the membrane material over the valve seat area increases the amount of force that is required to perform the valving function which results in a reduction in the efficiency of the fluid control device.
Accordingly, a need has arisen to reduce, if not eliminate, the deleterious effects of the aforementioned lateral displacement of the membrane.
Additionally, the membrane serves to seal the chamber and any associated grooves or channels opening through the adjacent surface. Conventionally, the membrane is simply allowed to compress between the valve cove and valve body wherein the entire membrane acts in the sealing capacity. This relatively large area of contact results in a substantial likelihood of leakage and increases the cubic volume of the membrane displaced for a given amount of compression. The present invention localizes the compressing forces to form a sealing engagement along a narrow band surrounding the areas to be sealed. Thus, the cubic volume of membrane displaced for a given amount of compression is kept to a minimum while, at the same time, functioning to seal the chamber and any associated openings.